Which is correct - "look up words in the dictionary" or "look words up in the dictionary"?

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I teach a special ed. reading program. I think one of the exercises in the workbook is wrong. We are working with phrasal verbs - look up, throw away, turn over, etc. The sentences in the exercise have the two parts separated. An example is: "Throw the trash out." I think it should be "Throw out the trash." Which is correct or does it matter?